This application is based on Japanese Patent Application HEI 11-76800, filed on Mar. 19, 1999, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to a liquid crystal display device and its manufacture method, and more particularly to an active matrix type liquid crystal display device and its manufacture method.
b) Description of the Related Art
An active matrix type liquid crystal display device has a number of pixels disposed in a matrix shape in a display area. Each pixel includes a switching element and a pixel electrode. As a switching element, a thin film transistor (TFT) made of amorphous silicon is used. Scan lines and signal lines crossing each other are disposed in the display area to drive TFT of each pixel, the scan lines being connected to the gate electrodes of TFTs and the signal lines being connected to source electrodes of TFTS (ones of current electrodes which are herein called source electrodes as expedient).
A liquid crystal display device includes a TFT substrate, a common electrode substrate disposed opposing the TFT substrate, and a liquid crystal layer sandwiched between both the substrates. The common electrode substrate has a single common electrode formed in the whole display area. For color display, a color filter is formed on one of the substrates.
In a liquid crystal display device having an amorphous TFT at each pixel, a control circuit for scan lines and signal lines is disposed on a printed circuit board different from the TFT substrate, and connected to the TFT substrate by tape automated bonding (TAB). A control circuit for ICs and the like is also formed on a TAB film.
Although some point defects of a liquid crystal display device are permitted, line defects are not permitted. Therefore, even if a single scan line or single signal line is disconnected, the liquid crystal display device is considered as a defective product.
In order to repair such a line defect, repair operational (OP) amplifiers are connected in an external circuit. Each operational amplifier is structured to be connectable to a selected scan line or signal line, on the side opposite to the end of the scan line or signal line connected to a control circuit. For example, if one scan line is disconnected at its intermediate position, a signal from a scan line driver circuit can be transferred only to the disconnection point. By supplying an output of the OP amplifier from the other end of the same scan line, the disconnected scan line can be driven by the same signal. A disconnection of a signal line can be repaired in a similar manner.
In repairing a defect, hot wiring lines such as scan lines and signal lines are disposed crossing repair wiring lines, with an insulating film being interposed therebetween, and a laser beam is applied to a cross point to short-circuit the hot and repair wiring lines.
With this repair method, one external OP amplifier is required in order to repair one defect of a wiring line. As a number of OP amplifiers are connected, not only the manufacture cost rises but also the area to be occupied by OP amplifiers is required, so that the restrictions on design increase.
Recently, techniques have been developed by which an amorphous silicon film is converted into a polysilicon film by applying a laser beam such as XeCl laser and KrF laser to the amorphous silicon film formed on a glass substrate. If a polysilicon film is formed on a glass substrate, a high performance TFT can be formed.
At the same time when such a high performance TFT is formed, a peripheral circuit as well as the display unit can be formed on a glass substrate. Even in the case wherein the display unit with an integrated peripheral circuit is formed on a glass substrate, a defect repair by using OP amplifiers in an external IC may be performed. However, the electrical characteristics and temperature characteristics are greatly different between MOSFETs in OP amplifiers using single crystal silicon and polycrystalline TFT on a glass substrate. It is therefore difficult to repair a line defect to the degree that a substantial problem will not occur.
If upper and lower wiring layers with an interposed insulating film are to be short-circuited through laser radiation, the radiation energy sufficient for forming a good short-circuit is relatively high, and its margin is relatively narrow. Therefore, a repair success rate is low and latent cause of defects may be generated.
As described above, various kinds of problems are associated with a defect repair for an active matrix type liquid crystal display device.
It is an object of the present invention to provide a liquid crystal display device capable of easily repairing a defect.
It is another object of the present invention to provide an active matrix type liquid crystal display device with an integrated peripheral circuit, capable of easily repairing a defect which results in a line defect.
It is still another object of the present invention to provide a manufacture method for an active matrix type liquid crystal display device with an integrated peripheral circuit, capable of easily repairing a defect.
According to one aspect of the present invention, there is provided a liquid crystal display device, comprising: a first substrate having an insulating surface; a display unit disposed in a central area of the first substrate and including a plurality of pixels disposed in a matrix shape, a plurality of scan lines for activating pixels disposed in a row direction, and a plurality of signal lines each for transferring video data to an activated pixel among pixels disposed in a column direction; a scan line driver circuit formed in a first row direction side area of a peripheral area of the first substrate outside of the display unit, the scan line driver circuit generating a signal for driving the scan lines; a signal line driver circuit formed in a first column direction side area of the peripheral area of the first substrate, the signal line driver circuit generating a signal for driving the signal lines; and a repair circuit formed in a partial area of the peripheral area of the first substrate, the repair circuit having substantially a same structure as a portion of the scan line driver circuit and the signal line driver circuit.
According to another aspect of the present invention, there is provided a method of manufacturing a liquid crystal display device, comprising: a preparing step of preparing a TFT substrate having: a first substrate having an insulating surface; a display unit disposed in a central area of the first substrate and including a plurality of pixels disposed in a matrix shape, a plurality of scan lines for activating pixels disposed in a row direction, and a plurality of signal lines each for transferring video data to an activated pixel among pixels disposed in a column direction; a scan line driver circuit formed in a first row direction side area of a peripheral area of the first substrate outside of the display unit, the scan line driver circuit generating a signal for driving the scan lines; a signal line driver circuit formed in a first column direction side area of the peripheral area of the first substrate, the signal line driver circuit generating a signal for driving the signal lines; and a repair circuit formed in a partial area of the peripheral area of the first substrate, the repair circuit having substantially a same structure as a portion of the scan line driver circuit and the signal line driver circuit; and a repairing step of activating the repair circuit by using the repair line when a defect is found, to repair the defect.